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Old 09-06-2011, 01:06 AM   #1
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Attic ventilation - Have enough? Am I correct that there isn't much?


My questions might seem pretty basic, but I know a lot of people screw up ventilation, so I want to make sure to get it right. Thanks a bunch for your time!

My attic has one peak, sloping toward the front and back of the house. The sides of the attic are straight up to the peak, and each side has a gable vent.

I think the pictures below show that my attic's ventilation only consists of 2 gable vents, quite a few (5-10?) grill vents through roof of around 8-10" diameter, and a limited area of soffit vents only on the front overhang.

QUESTION 1 - Am I right, that with the gutters so close to the house, that there's no ventilation (like a soffit) being provided on the back of the house, and the front of the house where the overhang isn't? If this is correct, than this means seal up and insulate the area fully without using any baffles? (But of course using baffles at the overhang)

QUESTION 2 - Looking down the side exterior walls, they appear to be packed (perhaps also with rock woll.) No ventilation here either, so fill up the last 6" or so, and insulate the area fully without using any baffles?

QUESTION 3 - Is what's here adequate ventilation, or do we need to add something else?



Front of house - The area with an overhang, with soffit vents





Front of house - The area without an overhang, no soffit vents





Back of house - No overhang, no soffit vents





Side of the house - Each has a gable vent





In attic - Looking toward back of the house.
Might be hard to see, but the drywall goes to a piece of wood laying flat, and then there's a drop-off area of a few inches






In attic - Looking down side exterior wall (a soffit [typo-meant gable] vent is directly above us.)


Last edited by darlingm; 09-07-2011 at 03:15 AM.
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Old 09-06-2011, 09:43 PM   #2
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Attic ventilation - Have enough? Am I correct that there isn't much?


This on figuring your venting; http://www.airvent.com/homeowner/pro...it-specs.shtml

1. Where are you located?

2. There is no top plate on the frame wall of the cavity pictured?
3. Why does the insulation not fill up the wall closer than 18"?

4. How deep is the overhang with the punched vents 32" apart?

Gary

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Old 09-07-2011, 02:20 AM   #3
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Attic ventilation - Have enough? Am I correct that there isn't much?


Quote:
Originally Posted by GBR in WA View Post
This on figuring your venting; http://www.airvent.com/homeowner/pro...it-specs.shtml

1. Where are you located?

2. There is no top plate on the frame wall of the cavity pictured?
3. Why does the insulation not fill up the wall closer than 18"?

4. How deep is the overhang with the punched vents 32" apart?

Gary
1. Located in the Detroit, MI area.

2. Correct. It appears my house, built in 1958, used something called balloon framing - where 2x4's extend vertically from the foundation sill all the way up into the roof. (... I guess they apparently liked the idea of quickly spreading fires.)

3. Don't think I'm 100% understanding your question. If you mean why does the insulation in the exterior wall that is open in the attic due to balloon framing not filled all the way to the top, I really don't know. I think there's only 6" or so missing from the top, perhaps it settled that much overtime, but that seems like a lot of settling.

4. The overhang is 2 feet.
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Old 09-07-2011, 03:13 AM   #4
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Attic ventilation - Have enough? Am I correct that there isn't much?


Quote:
Originally Posted by GBR in WA View Post
This on figuring your venting; http://www.airvent.com/homeowner/pro...it-specs.shtml

1. Where are you located?

2. There is no top plate on the frame wall of the cavity pictured?
3. Why does the insulation not fill up the wall closer than 18"?

4. How deep is the overhang with the punched vents 32" apart?

Gary
1. Located in the Detroit, MI area.

2. Correct. It appears my house, built in 1958, used something called balloon framing - where 2x4's extend vertically from the foundation sill all the way up into the roof. (... I guess they apparently liked the idea of quickly spreading fires.)

3. Don't think I'm 100% understanding your question. If you mean why does the insulation in the exterior wall that is open in the attic due to balloon framing not filled all the way to the top, I really don't know. I think there's only 6" or so missing from the top, perhaps it settled that much overtime, but that seems like a lot of settling.

4. The overhang is 2 feet.
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Old 09-07-2011, 07:20 AM   #5
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Attic ventilation - Have enough? Am I correct that there isn't much?


I would be surprised if your single 1958 story was balloon framed. it looks to me like the picture of the gabled end wall cavity is open only from where the brick 1st floor meets the gabled end??
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Old 09-07-2011, 07:59 AM   #6
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Attic ventilation - Have enough? Am I correct that there isn't much?


Can you post a picture of the roofline of the front of the house that would include the overhang ..

Are the perforated vents in the front overhang totally open to the attic or is there plywood above with holes cut in it?

How many of the perforated vents are there?

The front overhang looks deeper than 2'.

Exactly how many through the roof vents do you have?

What is the square footage of your house?

Do you have re-roof planned in the near future?

Last edited by josall; 09-07-2011 at 08:08 AM.
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Old 09-07-2011, 10:31 AM   #7
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Attic ventilation - Have enough? Am I correct that there isn't much?


QUESTIONS

1. Is my current attic ventilation screwed up, by having two ventilation methods which are so-so by themselves, but together are counteracting each other?

It is not ideal but not every home requires soffit venting to be adequate.

2. Before I add the new cellulose insulation, what changes should I make to the ventilation?

Totally depends on what you are wanting to spend and do. The fact that you don't appear to have mold or mildew indicates that your soffit venting is adequate but not ideal. Attic ventilation is for moisture control and not roof temperature modulation.

NOTE: I need to lean toward quicker fixes. I'm doing this myself, but am recovering from back problems from a car accident, so can't get into something too involved.

The things I've considered are:

a) Leaving things be, and blowing in the additional cellulose

b) Trying to improve the opposing gable vent system, by blocking off the soffit vents and box vents. Although this would make the gables more effective, I have no idea if this would do more harm than good overall.

No. Do not do this. Attic ventilation should be balanced, however, if you are going to error on one side or the other, you should have more intake air than exhaust air. By blocking off the soffits, you will further exacerbate the issue and create more stack effect in the attic and draw more conditioned air out of the space below. Do not block off your soffits.

c) Trying to improve the soffit/box vent system, by blocking off the gable vent nearest the soffit vent.

I would leave well enough alone for right now. What you have has worked so far. If you were going to add anything, you might try more eave venting via a vented fascia board or similar.

d) Something else? The gable vents are pretty small - perhaps using an exhaust fan on one, or that plus an intake fan on the other? Perhaps adding box vents closer to the bottom of the roof to act as soffits?

Avoid powered attic fans as they usually create more than solve problems.

Properly air sealing the attic floor and sealing up any penetrations will mitigate your necessity for attic ventilation and allow your current arrangement to be more adequate. It will also help with utilities, comfort, and overall efficiency. I would do this prior to adding cellulose.
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Old 09-07-2011, 04:01 PM   #8
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Attic ventilation - Have enough? Am I correct that there isn't much?


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Originally Posted by 1910NE View Post
I would be surprised if your single 1958 story was balloon framed. it looks to me like the picture of the gabled end wall cavity is open only from where the brick 1st floor meets the gabled end??
That's certainly possible. I had assumed the insulation I can see goes all the way down the wall and had settled quite a bit, but perhaps there's only a few inches there on top of brick. I'll have to take a look at that up there in a bit. Thanks for the idea!
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Old 09-07-2011, 04:28 PM   #9
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Attic ventilation - Have enough? Am I correct that there isn't much?


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Originally Posted by josall View Post
Can you post a picture of the roofline of the front of the house that would include the overhang ..

Are the perforated vents in the front overhang totally open to the attic or is there plywood above with holes cut in it?

How many of the perforated vents are there?

The front overhang looks deeper than 2'.

Exactly how many through the roof vents do you have?

What is the square footage of your house?

Do you have re-roof planned in the near future?
Pictures are below of the roofline in the front including the overhang. Pictures are also below of the front overhang view from the attic. You'll see a reflective insulation sort of blocking off the overhang's roof "bulge", with a gap at the top. So, unfortunately, I can't see what's directly above the soffit vents. There are 5 pairs of perforated vents in the overhang, so 10 perforated vents total. They're about 8" across, and go along the whole 3 feet overhang.

Just measured the front overhang, and you're right. It's 3 feet.

I have 7 through the roof vents. Picture of the back of the house is below.

Square footage is 1034sqft.

Realistically, re-roofing is something we'll do when absolutely necessary, rather than for efficiency or aesthetics. Budget is very tight. I'm not exactly sure when the roof was re-done. We purchased from a house repairer/flipper, so I didn't get to speak to the person who previously lived in the home. Home inspector guessed it is around 7 years old. Neighbor believes it was more like 4 years, but I know how some people (like me!) are bad at guessing number of years.



Front of the house - showing bulge in roof with overhang





Front of the house - showing roofline with overhang





Front of the house - The area with an overhang, viewed from the inside. There's reflective insulation blocking most of the area, but there is open room at the top to allow airflow. I'll measure, but I think this reflective insulation will act as its own baffle.





Back of house - Showing the 7 "box vents"

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Old 09-08-2011, 04:11 PM   #10
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Attic ventilation - Have enough? Am I correct that there isn't much?


You should have 7sq.ft of ventilation for your attic. You currently have approx. 3.5 sq.ft. of exhaust (at the peak) which is exactly what you need. So I wouldn't make any changes there. You are short on the intake side (the soffit) you need 3.5 sq.ft. and you barely have .50 sq.ft. in your front overhang. You would need to add the equivalent of 7- 8x16 soffit vents with a net free area of 65 sq.in. to give you a balanced system.. Without doing something major the only place to add while not ideal is your front overhang. It's really not broke so why fix. I would cut back that foil board to make sure you are not bottle necking any intake you have from your overhang.

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